Re: unbelievably bad performance: 2.6.27.37 and raid6

From: "NeilBrown" <neilb@suse.de>
To: Michael Evans <mjevans1983@gmail.com>
Cc: Jon Nelson <jnelson-linux-raid@jamponi.net>,
	LinuxRaid <linux-raid@vger.kernel.org>
Subject: Re: unbelievably bad performance: 2.6.27.37 and raid6
Date: Tue, 3 Nov 2009 20:16:20 +1100	[thread overview]
Message-ID: <4b0dc4f875f3c6e21de0f9e3f5bbc0b4.squirrel@neil.brown.name> (raw)
In-Reply-To: <4877c76c0911022246m78736f5co412530c456031139@mail.gmail.com>

On Tue, November 3, 2009 5:46 pm, Michael Evans wrote:
>> It is possible to get it fast than it is by increasing the
>> array's stripe_cache_size and also increasing the 'backup' size
>> that mdadm uses.  mdadm-3.1.1 will try to do better in this respect.
>> However it will still be significantly slower than e.g. a resync.
>>
>> NeilBrown
>>
>
> Sorry, one more Q: I was able to find strip_cache_size, and already
> asked about stripe_cache_active (and if setting it to 1 was safe); but
> I can't seem to even find the 'backup' size variable mentioned
> anywhere.  I'm going to start looking at the code next, but is it
> supposed to be in documentation?

It is in the code in mdadm, in 'Grow.c'.
It is called 'blocks' I think.  I'm not sure off hand what the units are.

NeilBrown

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